This invention relates to a microwave delay equalizer for use in a microwave communication system.
In a microwave communication system and, more particularly, a microwave multiplex frequency modulation communication system, a delay distortion inevitably occurs due to an unequal or nonlinear time delay at a transmitter and/or a receiver of the system. Control of the delay distortion becomes more important because the delay distortion is liable to increase with transmission capacity of the microwave communication system. The delay distortion is usually compensated by the use of a microwave delay equalizer for rendering the time delay equal or flat as a whole. Inasmuch as the time delay is represented by the derivative of a phase shift with respect to frequency, the delay equalizer compriser one or more reactance elements for making the phase shift versus frequency characteristic linear over a given bandwidth.
As will later be described with reference to one of several figures of the accompanying drawing, a conventional microwave delay equalizer of the type described comprises a circular having three ports with a resonator connected to one of the three ports as the reactance element. However, the circulator is usually made of ferrite, the characteristics of which are considerably dependent on temperature. Accordingly, temperature compensation is indispensable. An alternative conventional delay equalizer comprises a hybrid directional coupler having a pair of additional ports besides an input and an output port. A pair of resonant cavities are connected to the respective additional ports as the reactance elements, as will later be described with reference to another figure of the accompanying drawing. The alternative conventional equalizer is bulky and heavy due to the two resonant cavities.